JP2557758B2 - Exhaust gas treatment method using microalgae - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating exhaust gas with microalgae, and more particularly to a method for immobilizing carbon dioxide and nitrogen oxides in combustion exhaust gas using microalgae.

[0002]

2. Description of the Related Art It is said that CO ₂ has the highest contribution rate among the greenhouse gases that cause global warming. C
Immobilization of CO ₂ using photosynthesis of microalgae has been proposed as one of O ₂ removal technologies, and the application of chlorella, which is well known in the past, has been promoted. In addition, various culturing devices have been manufactured as reactors, and an aeration flow type photoreaction tank that can always adjust the optimum culturing conditions has been prototyped.

[0003]

In the treatment of exhaust gas from plants, denitration, desulfurization and heat recovery are carried out.
However, the temperature of the exhaust gas is usually a high temperature of hundreds of tens or more for the purpose of preventing white smoke. Further, due to the water vapor partial pressure and the like, a large amount of energy is required to reduce the exhaust gas temperature to 40 to 50 ° C. or less, and in this case, the effect of heat recovery cannot be expected. Therefore, the lower limit of the practically feasible final exhaust gas temperature is estimated to be 40 to 50 ° C. On the other hand, when using conventional chlorella or the like, the reaction temperature is 20
It was necessary to adjust the temperature to -25 ° C, and it was difficult to control the inflowing exhaust gas or the cooling temperature of the reactor.

Further, the pH in the reaction tank is lowered by NOx, SOx, etc. in the combustion exhaust gas, but the proper growth pH of chlorella etc. is in the neutral range, and the activity is remarkably lowered in the strongly acidic range. Equipment for adjusting the pH is required. Thus, there is a problem in adjusting the treatment environment, which is one of the causes that make it difficult to put the CO ₂ fixing technique using microalgae into practical use. In view of the above problems, the present invention provides SOx
And / or an exhaust gas treatment method using microalgae capable of stably removing carbon dioxide and nitrogen oxides even under high temperature and strongly acidic conditions generated by aeration of combustion exhaust gas containing NOx. Is an issue.

[0005]

In order to solve the above problems SUMMARY OF THE INVENTION In the present invention, the culture allowed to coexist with a single species or more acidophilic microalgae as liquids medium and microalgae, light Supplying SOx and / or NOx while maintaining room temperature
By venting the combustion exhaust gas containing, in which the exhaust gas treatment method for removing carbon dioxide of at least the exhaust gas.
Further , in the present invention, SOx and / or SOx and / or while maintaining a high temperature under the supply of light to a culture medium in which a liquid medium and a single species or a plurality of species of acidophilic thermophilic microalgae as microalgae coexist
Is vented combustion exhaust gas containing NOx, it is obtained by the exhaust gas treatment method for removing carbon dioxide of at least the exhaust <br/> gas.

As mentioned above, the present invention is intended for exhaust gas.
Be2Have specific physiological characteristics for each of the two situations
It applies a group of microalgae.  Culture with NOx, SOx, etc. existing in the exhaust gas
When the liquid becomes strongly acidic, the temperature of the reaction tank is maintained at room temperature.
A single species of eosinophilic microalgaeorIs a multiple species
CO in the exhaust gas maintained under aeration₂Fixed to the algal body
Remove. For example, cyanidal caldarium (C
yanidium caldarium) has a pH of 1.
Good growth or CO in 5 to 3₂Indicates fixed. Other than the same kind,
Acidophilic microalgae are classified into various groups such as green algae, red algae, and diatoms.
Known to the group (literature1, Extreme environmental microorganism handbook
Ku Yasuo Oshima 91 Science Forum Co., Ltd. An example
As Nichia Palea (Nitzschia pa
lea) and the like. These algae are NO in water₃ ⁻
Are known to be used for their growth (see above document
1), N generated in the exhaust gas is dissolved in the culture solution to generate N
O₃ ⁻Is fixed to the alga body, CO₂At the same time nitrogen
It is possible to remove oxides. Figure 2 shows the above cyanidiu
Mu Caldarium (Cyanidium caldar)
ium) is NH₄ ⁺Same as NO₃ ⁻To also absorb
It is a graph shown.

[0007]  NOx, SOx, etc. existing in exhaust gas
When the culture solution becomes strongly acidic due to
Single species of algaeorIs a high temperature (preferably
The temperature of the exhaust gas is kept at 40 to 80 ° C.₂
Is fixed to the alga body and removed. Cyanideum Cal mentioned above
Dalium (Cyanidium caldarium)
Shows good growth under the temperature condition of 30 to 35 ° C.,
It grows even under high temperature conditions of ~ 60 ° C. Figure 3,Growing condition
It is a graph which shows. For such acid- and thermophilic microalgae
Is,Other examples include Clococci diopsis sp. (Ch
roococcidiopsis sp. ) Etc.
Be done.

It should be noted that these microalgae can be used in any form of life such as adherence and floating, but in recent years, an aerated fluidized bed type efficient photoreaction tank has been prototyped and its use has been proposed. Therefore, it is preferable to use planktonic algae that have good light utilization. Further, in setting the reaction tank, any of a method of inoculating the medium in the reaction tank with the alga and growing it inside, or a method of separately supplying a large amount of green algae and the medium to the reaction tank may be used. In addition, it is sufficient for the medium to appropriately supply the components necessary for the growth of the algae, and it is preferable to use the components supplied by the exhaust gas, the waste liquid, etc. Does not need

[0009]

It is known that plants containing microalgae perform photosynthesis, immobilize CO ₂ on algae and products, and absorb compounds such as nitrogen and phosphorus to construct algae. In addition, the following relationships are generally found between flora and phytoplankton and nutrients in the ocean. This relationship holds in almost all sea areas, and it is also known that it is extremely convenient when looking at the flow of elements between the organisms called phytoplankton and the chemical components called nutrients.

When NOx in the exhaust gas dissolves in water, NO ₃ is produced as follows. Microalgae The NO ₃ ^- using nitrogen, which is capable of growing as a nitrogen source. Further, the conventional microalgae, around room temperature, pH also show good growth in the vicinity of almost neutral, are known microalgae group shown good growth in special environments, we use in the present invention good Microalgae that are acidic and acidophilic and thermophilic are also one of them. Since these maintain their function even under high temperature and strongly acidic conditions caused by ventilation of exhaust gas,
The burden of pH adjustment can be reduced. The surplus algal bodies and metabolites of these algae can be separated from the processing device and used as resources such as recovery of useful substances and fertilization.

[0011]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. Example 1 An experiment relating to the removal of carbon dioxide was carried out by using Nitzschia pal, which is an acidophilic microalgae.
Chlorella which is a common algae
Pyrenoidosa (Chlorella pyrenoi)
dosa) was used as a control, and the cells were cultured at pH 2.0 and a temperature of 25 ° C. The medium used was a Csi modified medium. The composition is shown below. _{Ca (NO 3) 2 · 4H} 2 O 150 mg KNO 3 100 mg β-Na 2 glycerophosphate _{50 mg MgSO 4 · 7H 2 O} 40 mg Vitamin B12 0.1 [mu] g biotin 0.1 [mu] g Thiamine HCl 10 [mu] g PIV metal 3 ml 1 , 2,3,4-cyclopentane tetracarboxylic acid _{500 mg Na 2 SiO 3 · 9H} 2 O 100 mg 1 liter of distilled water

FIG. 1 shows a flow chart of the experimental apparatus. In FIG. 1, CO ₂ 1 and air 2 are mixed in a gas mixing tank 3 and introduced into a culture solution 6 in a photoreaction tank 5, CO ₂ is fixed in the culture solution 6 and a treated gas is discharged from 7. To be done. The culture solution was extracted from 8 and solid-liquid separated, and the separated solution was 10
The surplus algal bodies are extracted from 11, and the algal bodies are returned from 13 to the reaction tank. Fresh medium is supplied from 12, and the concentration of algal cells in the tank is kept constant. Reference numeral 14 is a gas measuring device for CO ₂ and / or NOx in the processing gas.

The experiment was conducted in a continuous system, and CO ₂ was added to the air at 5
% Mixture was aerated with 200 ml / l.min. The separated liquid was drawn out by solid-liquid separation, and the same amount of new medium was added to maintain the tank culture liquid amount at 1 liter. Since the algal cell concentration in the tank was kept constant at 5 g / l, the surplus algal cells were extracted.
The results are shown in Table 1 .

[Table 1]

Example 2 An experiment relating to the removal of carbon dioxide was carried out by using cyanidium cardarium (Cyanid)
chlorella pyrenoidosa (Chlore), which is a common algae.
lla pyrenoidosa) as a control, p
Culture was performed at H2.0 and a temperature of 55 ° C. (CC) medium was used as the medium. The composition is shown below. _{Ca (NO 3) 2 · 4H} 2 O 150 mg KNO 3 100 mg MgSO 4 · 7H 2 O 40 mg β-Na2 -glycerophosphate 50 mg Thiamine HCl 10 [mu] g vitamin B12 0.1 [mu] g biotin 0.1 [mu] g cyclopentanetetracarboxylic acid 500 mg PIV Metal 3 ml Distilled water 1 liter

The culturing method is in accordance with Example 1. The results are shown in Table 2.
Shown in

[Table 2]

In each of the above examples, the target chlorella pyrenoidosa (Chlorellapyren)
Oidosa) did not grow and died in all experimental plots . Is acidophilic microalgae Nitchea Palea (Nitzschia palea), a good eosinophilic thermophilic microalgae Shianidiumu caldarium (Cya
Nidium caldarium) each showed extremely good growth even under severe conditions. In addition to CO ₂ , NO of 0.1
When mixed with air to have a concentration of 10% and treated under the same conditions as in Examples 1 and 2 , NO was not detected in the treated air,
The removal rate was 100%. From this result, it is also possible to utilize nitrogen oxides in the waste gas as the N source of algae. When the amount of nitrogen oxides in the waste gas is insufficient for the amount of N required by algae, waste water or the like can be used as the N source.

[0017]

The present invention according to the present invention has two effects as follows. ( 1 ) Reduction of nitrogen oxide treatment process in exhaust gas treatment process.
By using eosinophilic microalgae, the exhaust gas containing nitrogen oxides is directly introduced into the reactor to adjust the pH of the culture solution.
It becomes possible to operate even if the value decreases. Further, since these algae can use nitrate nitrogen as a nitrogen source, it is possible to remove carbon dioxide and nitrogen oxides at the same time. (2) reduction of savings 及 beauty nitrogen oxides in the exhaust gas treatment process step of cooling energy of the exhaust gas. By using the acid-philic thermophilic microalgae, carbon dioxide and nitrogen oxides can be simultaneously removed at a temperature of 55 to 60 ° C at the maximum.

[Brief description of drawings]

FIG. 1 is a flow process diagram of an experimental apparatus for carrying out the method of the present invention.

FIG. 2 is a graph showing absorption of nitrogen compounds of cyanidin-cardarium.

FIG. 3 is a graph showing the growth state of cyanidium cardarium depending on the temperature.

[Explanation of symbols]

1: CO ₂ , 2: Air, 3: Gas mixing tank, 4: Gas introduction tube, 5: Photoreaction tank, 6: Culture solution, 7: Gas exhaust tube, 8:
Culture liquid drawing tube, 9: Solid-liquid separator, 10: Liquid drawing tube, 1
1: alga body extraction tube, 12: culture medium supply tube, 14: gas measuring instrument

Front Page Continuation (72) Inventor Etsuko Takizawa 4-2-1 Honfujisawa, Fujisawa City, Kanagawa Prefecture Ebara Research Institute, Ltd. (56) Reference JP-A-57-112870 (JP, A) JP-A-3- 154616 (JP, A)

Claims (2)

(57) [Claims] 1. SOx and / or NOx is supplied to a culture solution in which a liquid medium and a single species or plural species of acidophilic microalgae as microalgae coexist, while being kept at room temperature under the supply of light.
The combustion exhaust gas containing vented exhaust gas treatment method for removing carbon dioxide of at least the exhaust gas. 2. SOx and / or SOx and / or while maintaining a high temperature under the supply of light in a culture medium in which a liquid medium and a single species or a plurality of species of acidophilic thermophilic microalgae as microalgae coexist.
By venting the combustion exhaust gas containing NOx, exhaust gas treatment method for removing carbon dioxide of at least the waste gas <br/> during scan.